﻿//-----------------------------------------------------------------------
// <copyright file="IFuture.cs" company="Nathan Miller">
// Copyright (c) Nathan Miller.
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
// 
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
// </copyright>
//-----------------------------------------------------------------------
namespace TileTool.Threading.Future
{
    using System;

    /// <summary>
    /// Interface for a class which tracks the status of some operation that
    /// completes at some point in the future.
    /// 
    /// Users of this interface can poll for result completion by checking
    /// the State property or by using the OnComplete() function.
    /// </summary>
    public interface IFuture
    {
        #region Events

        /// <summary>
        /// Event triggered when there is progress in computing the final
        /// result for the future object.
        /// 
        /// The sender for the event will be the IFuture object and the event
        /// arguments will be a FutureProgressEventArgs object.
        /// 
        /// This event will be triggered on the same thread that the IFuture object
        /// was created on.
        /// </summary>
        event EventHandler<FutureProgressEventArgs> Progress;

        #endregion

        #region Properties

        /// <summary>
        /// Gets the state of the future object.
        /// </summary>
        FutureState State
        {
            get;
        }

        /// <summary>
        /// Gets if the future object has completed successfully.
        /// </summary>
        bool IsCompleted
        {
            get;
        }

        /// <summary>
        /// Gets if the future object has been canceled.
        /// </summary>
        bool IsCanceled
        {
            get;
        }

        /// <summary>
        /// Gets if the state of the future object is in an error.
        /// </summary>
        bool IsError
        {
            get;
        }

        /// <summary>
        /// Gets the error value for the future object. Only valid when 
        /// State is FutureState.Error.
        /// </summary>
        Exception Error
        {
            get;
        }

        #endregion

        #region Methods

        /// <summary>
        /// Method to call when the future is complete either via
        /// success of failure.
        /// 
        /// If a user of the future object calls this method after the
        /// state has been set to completed, error or canceled, the provided
        /// method should be called immediately.
        /// 
        /// The method will be called on the same thread that the IFuture object
        /// was created on.
        /// </summary>
        /// <param name="func">Method to call.</param>
        void OnComplete(Action<IFuture> func);

        /// <summary>
        /// Function called to cancel the computation of the future result.
        /// 
        /// If the future object has already been computed or is in an error state,
        /// this function will do nothing.
        /// 
        /// Cancel() should trigger a Completed event. Once canceled the Completed event
        /// should not be triggered again.
        /// </summary>
        void Cancel();

        #endregion
    }
}
